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Epoxy goes mainstream

While most woodworkers shy away from epoxy, furnituremaker
Robert Hensarling finds it the adhesive of choice in his workshop, and for good reason.

Robert relies on epoxy

Famed for his mesquite Texas-style rocking chairs, Robert Hensarling uses epoxy for just about all his assembly, regardless whether the furniture finds a home in a living or board room. What gives (or doesn't give) with epoxy? We asked Robert about his heavy reliance on it, seeking answers that you too can put to use in your shop.

Q: Why do you choose epoxy for your joinery?A: I like it because it maintains a little resiliency after curing. In other words, it expands and contracts as wood moves. I work mostly with mesquite, but find that epoxy also performs well with other woods I work including quilted maple and black walnut. Another advantage: Compared to yellow glues, it gives me more working time (approximately 15 to 30 minutes) for adjustments before it sets up.

Solvents and safety
Solvents for epoxy include acetone, lacquer thinner, denatured alcohol, and ordinary white vinegar. These work fine for cleaning tools, but not so well on skin because these thinners can permeate your pores. Robert always wears disposable latex gloves when he mixes, pours, dispenses, spreads, clamps, or cleans up epoxy. Also, work in a well-ventilated space or wear arespirator, he warns. Fumes from epoxies pose health hazards.

It's all in the mixing

Q: What do you mix the epoxy in, and how do you apply it?A: I mix the epoxy in throwaway plastic cups using wood sticks, such as paint stirrers and tongue depressors. To ensure that the depressors fully contact the cup side and bottom for thorough mixing, I square the round ends on a disc or belt sander. I apply the epoxy using the sticks and disposable glue brushes.

Removing the excess

Q: Epoxy can be messy. How do you deal with squeeze-out?A: I assemble everything rough, sanded with nothing finer than 60-grit paper. For a sculpted joint, such as between an arm and a leg, I let the epoxy cure overnight. Then I remove the squeeze-out with a die grinder, carbide grinding wheel, or a drill with a 60- or 80-grit sanding drum, as shown in the photo. Because I leave 1/16" to 1/8" extra stock to remove on curved joints for blending purposes after assembly, using a grinder or sanding drum also helps to sculpt the area to final shape. After grinding, I finish-sand the area using a palm sander with progressively finer grits of sandpaper.

For a square-edge butt joint, I remove excess epoxy using a paper towel right after clamping the parts together. When the epoxy cures, I sand the area to remove any remaining adhesive. I don't use acetone or other solvents, which can seep in and weaken joints or clog open wood pores.

Q: What types of epoxies do you use for joinery?A: For most joinery, I use System Three's General Purpose Epoxy. (Call 800/333-5514, or on the Web at systemthree.com.) It comes with a resin and a choice of three hardeners. In winter weather, I go with their fast hardener; at normal 60 degree to 100 degree temperatures, their medium hardener works well; on really hot Texas days, I use their slow hardener. Using the appropriate hardener gives me the needed open time to spread out, fine-adjust, and clamp joints.
For joints that I leave particularly loose, such as leg joints, I use System Three's T88 Structural Epoxy Adhesive instead of the General Purpose Epoxy because it's thicker and won't run out. (Because I test-fit these joints many times during construction, the loose fit reduces the chance of damaging the parts.) T88 epoxy comes with a resin and one hardener, and it cures in temperatures as low as 35 degrees.

Q: To fill gaps on surfaces, do you add sawdust to the epoxy?A: I prefer not to do this, and here's why. I've found that the epoxy color changes when you add sawdust, particularly with mesquite, which makes a repaired area more noticeable. I've tried adding tints to get a better color match, but found this unsatisfactory too. For me, using just the basic clear amber epoxy works best.

A drill with a sanding drum
quickly removes excess cured
epoxy and blends the joint
between this arm and leg.

The great gap filler

Q: How do you repair epoxied joints? By knocking them apart? A: You can't knock an epoxied joint apart as easily as one assembled with water-based glues. What I do instead when chair making is saw off a piece-say a back slat, flush at the seat and head crest. Then I drill out the joints, making the hole in the head crest twice as deep as the one in the seat, and epoxy a new slat in place. This same technique works for replacing an arm or a leg, but you must be very careful when cutting out the broken part to avoid removing stock at the joint from the adjoining part.

Q: Do you prepare a joint for epoxy differently than for yellow glue?A: Yes. One of the things I like about epoxy is that it lets me make what I call "floating dowel" joints. With these, I drill slightly oversize holes so the dowels have a loose fit. Epoxy fills the space around the dowels, as shown in the photo, which makes them stronger and lets me make adjustments when clamping the parts together. Another nice feature about epoxy is that it won't swell dowels or biscuits because there's no water in it.

Robert offers four-day seminars on rocking-chair building as well as one-on-one instruction. For more information, write Robert Hensarling, 4326 East Main Street, Uvalde, TX 78801, or visit his Web site: mesquiterocker.com

This arm/leg joint cutaway shows
how the epoxy encapsulates the
dowel in an oversize hole,
strengthening the dowel.